Retrospective studies have suggested a beneficial effect of lipid-lowering treatment on the progression of aortic stenosis (AS) in milder stages of the disease. In the randomized, placebo-controlled Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) study, 4.3 years of combined treatment with simvastatin 40 mg and ezetimibe 10 mg did not reduce aortic valve events (AVEs), while ischemic cardiovascular events (ICEs) were significantly reduced in the overall study population. However, the impact of baseline AS severity on treatment effect has not been reported. Baseline and outcomes data in 1,763 SEAS patients (mean age 67 years, 39% women) were used. The study population was divided into tertiles of baseline peak aortic jet velocity (tertile 1: ≤ 2.8 m/s; tertile 2: > 2.8 to 3.3 m/s; tertile 3: > 3.3 m/s). Treatment effect and interaction were tested in Cox regression analyses. The rates of AVEs and ICEs increased with increasing baseline severity of AS. In Cox regression analyses, higher baseline peak aortic jet velocity predicted higher rates of AVEs and ICEs in all tertiles (all p values < 0.05) and in the total study population (p < 0.001). Simvastatin-ezetimibe treatment was not associated with a statistically significant reduction in AVEs in any individual tertile. A significant quantitative interaction between the severity of AS and simvastatin-ezetimibe treatment effect was demonstrated for ICEs (p < 0.05) but not for AVEs (p = 0.10). In conclusion, the SEAS study results demonstrate a strong relation between baseline the severity of AS and the rate of cardiovascular events but no significant effect of lipid-lowering treatment on AVEs, even in the group with the mildest AS.